In an image forming apparatus, LED heads that generate electrostatic latent images on respective photosensitive drums are held on a pivotable upper cover by way of holding members, and the LED heads move, along with pivoting action of the upper cover between exposure positions where the photosensitive drums are exposed and retracted positions separated from the photosensitive drums. For example, JP-A-11-153893 describes such image forming apparatus and a lock mechanism (an open-close mechanism) for an upper cover. In the image forming apparatus, the mechanism releases a lock member as a result of pressing of an unlock button provided on an upper surface of a main body of the apparatus so that the mechanism lifts the upper cover to a predetermined height by means of a strong spring. And then, the upper cover is manually pivoted.
However, with the lock mechanism as mentioned above, the user has to perform two operations, that is, operation on the unlock button and pivoting movement of the upper cover. Further, since the strong spring for use in lifting the upper cover to the predetermined height is provided, the main housing of the apparatus and the upper cover have to be reinforced in order to maintain a locked state (a state where the upper cover is closed).